As an information storing device, a semiconductor memory device may be volatile or nonvolatile. A typical computer system may use a DRAM as a main memory and a hard disk drive and a nonvolatile memory (e.g., a flash memory) as an auxiliary storage device. An operating system program or an application program may be stored at an auxiliary storage device including a nonvolatile memory, and may be loaded onto a main memory at execution.
As a new memory device field develops, the nonvolatile memory may be used as the main memory instead of the DRAM. In this case, a problem may arise to implement a computer system with fast booting speed and less error using the main memory having the nonvolatile memory.